Here's why:
* Basicity and Metallicity: Basicity of oxides generally increases with increasing metallic character. Metals tend to form basic oxides, while nonmetals form acidic oxides.
* Trends in Group 5A: As you move down group 5A (Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth), the metallic character of the elements increases. This is due to the increasing atomic size and decreasing electronegativity.
* Bismuth Oxide (Bi₂O₃): Bismuth oxide is the most metallic oxide in group 5A and exhibits basic properties. It reacts with acids to form salts and with water to form bismuth hydroxide, which is a weak base.
Note: While the other elements in group 5A can form oxides, their oxides are generally more acidic or amphoteric (reacting with both acids and bases).
